CN101867041A - Synthesis method of high-purity fluorine-doped lithium iron phosphate anode material - Google Patents

Abstract

The invention relates to a synthesis method of high-purity fluorine-doped lithium iron phosphate anode material, which belongs to the field of the electro-chemistry energy storage material. The invention relates to an F-doped in-situ wrapped LiFePO4 material, i.e. LiFe(PO4)1-x/3Fx/C material. Analytical reagent LiOH.H2O, FeC2O4.2H2O, NH4H2PO4 is mixed with fluoride, carbon source is added into the mixture, and the mixture is spherically ground and dried to obtain a precursor. The precursor which is obtained in the previous step is roasted in two steps, and the precursor is firstly pre-heated and then is further roasted to obtain the product. The method has the advantages of low cost of raw materials, simple synthesis process, easy realization, high purity of product, high yield and the like; and has high magnification discharging performance and low-temperature discharging performance, and greatly improves the magnification performance, platform voltage and low-temperature performance of the LiFePO4 battery.

Description

A kind of synthetic method of high-purity fluorine-doped lithium iron phosphate anode material

Technical field

The present invention relates to a kind of controllable synthesis method of high-purity fluorine-doped lithium iron phosphate anode material, belong to field of electrochemical energy storage materials.

Background technology

As the anode active material of lithium ion battery of new generation of tool development and application potentiality, olivine structural is phosphate-based (as LiFePO ₄) have advantages such as cheap, environmentally friendly, that cycle performance is good, fail safe is outstanding.Yet, limit the biggest obstacle that this material is used, be its electronic conductivity and Li ⁺The chemical diffusion coefficient is all lower, and it is bigger to make it when heavy-current discharge capacity attenuation.Therefore, how to improve diffusion coefficient, the ionic conductivity of lithium ion and improve LiFePO ₄The high rate during charging-discharging of material is to make its practicability problem demanding prompt solution.

Current LiFePO ₄Material measure synthetic and study on the modification mainly concentrates on the technologies such as adding electric conducting material, doping and nano material preparation.Mainly be at LiFePO at present ₄In mix some foreign ion, cause LiFePO ₄Lattice forms defective, is formed with to be beneficial to Li ⁺The environment of diffusion.At present, the doping preparation method of having studied mostly concentrates on and replaces cation position, comprises LiFePO ₄Lithium position, iron position are carried out part and are replaced.Liao Xiaozhen etc. are in that " F replaces LiFePO ₄The influence of the chemical property of/C positive electrode " in the literary composition, a kind of F doping vario-property research method has been proposed, synthesize LiFe (PO ₄) _1-xF _3x/ C, this method effectively improves the chemical property of material, but the used prices of raw and semifnished materials costliness of this method, and products therefrom purity is not high, fails to be used widely.

Summary of the invention

The objective of the invention is to have used prices of raw and semifnished materials costliness, and problem such as products therefrom purity is not high, and a kind of controllable synthesis method of high-purity fluorine-doped lithium iron phosphate anode material is provided in order to solve the traditional F doping modification method.

The objective of the invention is to be achieved through the following technical solutions:

A kind of lithium ion battery of the present invention is with mixing fluorine LiFePO ₄The preparation method of electrode material, the expression formula of this material is:

LiFe(PO ₄) _1-x/3F _x/C(x＝0～3)

Its concrete steps are as follows:

Step 1: with analytical reagent LiOHH ₂O, FeC ₂O ₄2H ₂O, NH ₄H ₂PO ₄Mixing with fluoride, add carbon source, is medium with the absolute ethyl alcohol, and with rotating speed 300～450r/min high speed ball milling 10～15h, dry 10～20h makes mixture.

Step 2: with the mixture that makes in the step 1, under argon gas atmosphere, be warming up to 300～400 ℃ with 10～15 ℃/min earlier, behind insulation 5～10h, rise to 600～800 ℃ with 10～15 ℃/min again, calcining 10～20h, calcining is finished and is taken out after the afterreaction thing naturally cools to room temperature, obtains target product.

Wherein, LiOHH ₂O, FeC ₂O ₄2H ₂O, NH ₄H ₂PO ₄And the mol ratio between the fluoride is: (1.02-x): 1: (1-x/3): x, wherein x=0～3;

Described fluoride is LiF, NaF, KF, CaF ₂, MgF ₂Deng in one or more, it is in sucrose, glucose, the carbon black etc. one or more that carbon coats used carbon source, carbon coating ratio accounts for gross mass 2%～20%.

Beneficial effect

The present invention by two step solid phase methods synthetic mix fluorine LiFePO ₄Material has that the prices of raw and semifnished materials are cheap, synthesis technique is simple, realize products therefrom purity height, productive rate advantages of higher easily.Wherein, employed raw material FeC ₂O ₄2H ₂The O stable performance, NH ₄H ₂PO ₄Have low-corrosiveness, P source compound and Fe source compound are independent separately simultaneously, help to generate in proportion in course of reaction needed LiFePO ₄, and help realizing the controllability of fluorine ion selective doping and product molecular structure.In building-up process, ball milling is for raw material can fully be mixed, and first step pre-burning is for raw material are fully decomposed, and the calcining of second step is in order to generate the LiFePO that fluoridizes of complete in crystal formation ₄Particle.

X-ray diffraction analysis (XRD) shows that end-product has complete olivine-type LiFePO ₄Crystal structure.Charge-discharge test is the result show, F mixes and improved LiFePO ₄The high-rate discharge ability of/C material and low temperature performance, during F doping x=0.02, the discharge capacity of 10C multiplying power is equivalent to 81.81% of 1C multiplying power discharging capacity, still can emit 75% of normal temperature capacity-20 ℃ of temperature 0.1C multiplying powers.If this material is applied to lithium ion battery, will greatly improve LiFePO ₄The high rate performance of battery, platform voltage and cryogenic property can solve LiFePO well ₄The subject matter that battery exists at present.

Description of drawings

Fig. 1 is end-product LiFePO ₄The XRD of/C material, embodiment 1 product, embodiment 2 products, embodiment 3 products, embodiment 4 products is collection of illustrative plates relatively;

Fig. 2 is end-product LiFePO ₄The 0.1C first of/C material, embodiment 1 product, embodiment 2 products, embodiment 3 products, embodiment 4 products discharges and recharges comparison curves;

Fig. 3 is end-product LiFePO ₄The discharge capacity comparison curves of circulation time continuously under different multiplying of/C material, embodiment 1 product, embodiment 2 products, embodiment 3 products, embodiment 4 products;

Fig. 4 end-product LiFePO ₄The cyclic voltammetry curve of/C material, embodiment 2 products;

Fig. 5 end-product LiFePO ₄The AC impedance spectrogram of/C material, embodiment 2 products;

Fig. 6 end-product LiFePO ₄/ C material, the embodiment 2 products continuous discharge capacity of circulation time under the different multiplying when-20 ℃ of temperature;

Fig. 7 end-product LiFePO ₄/ C material, the AC impedance spectrogram of embodiment 2 products when-20 ℃ of temperature.

Embodiment

Embodiment 1

LiFe (PO ₄) _0.996F _0.01The preparation of/C material

Step 1: with analytical reagent LiOHH ₂O, FeC ₂O ₄2H ₂O, NH ₄H ₂PO ₄And LiF, according to stoichiometric proportion 1.01: 1: 0.996: 0.01 mixed, and adds the sucrose of end-product quality 10%, is medium with the absolute ethyl alcohol, with rotating speed 450r/min high speed ball milling 11h, makes mixture behind the dry 15h in ball mill.

Step 2: with the mixture that makes in the step 1 porcelain Noah's ark of packing into, in tube furnace, under argon gas atmosphere, be warming up to 350 ℃ with 10 ℃/min earlier, behind the insulation 7h, rise to 650 ℃ with 10 ℃/min again, sintering 15h treats to take out when product is cooled to room temperature, promptly gets end-product.

Embodiment 2

LiFe (PO ₄) _0.993F _0.02The preparation of/C material

Step 1: with analytical reagent LiOHH ₂O, FeC ₂O ₄2H ₂O, NH ₄H ₂PO ₄And LiF, according to stoichiometric proportion 1: 1: 0.993: 0.02 mixed, and adds the sucrose of end-product quality 10%, is medium with the absolute ethyl alcohol, with rotating speed 450r/min high speed ball milling 11h, makes mixture behind the dry 15h in ball mill.

Step 2: with the mixture that makes in the step 1 porcelain Noah's ark of packing into, in tube furnace, under argon gas atmosphere, be warming up to 300 ℃ with 10 ℃/min earlier, behind the insulation 5h, rise to 650 ℃ with 10 ℃/min again, sintering 10h treats to take out when product is cooled to room temperature, promptly gets end-product.

Embodiment 3

LiFe (PO ₄) _0.99F _0.03The preparation of/C material

Step 1: with analytical reagent LiOHH ₂O, FeC ₂O ₄2H ₂O, NH ₄H ₂PO ₄And LiF, according to stoichiometric proportion 0.99: 1: 0.99: 0.03 mixed, and adds the sucrose of end-product quality 10%, is medium with the absolute ethyl alcohol, with rotating speed 450r/min high speed ball milling 11h, makes mixture behind the dry 15h in ball mill.

Step 2: with the mixture that makes in the step 1 porcelain Noah's ark of packing into, in tube furnace, under argon gas atmosphere, be warming up to 350 ℃ with 15 ℃/min earlier, behind the insulation 6h, rise to 650 ℃ with 15 ℃/min again, sintering 12h treats to take out when product is cooled to room temperature, promptly gets end-product.

Embodiment 4

LiFe (PO ₄) _0.987F _0.04The preparation of/C material

Step 1: with analytical reagent LiOHH ₂O, FeC ₂O ₄2H ₂O, NH ₄H ₂PO ₄And LiF, according to stoichiometric proportion 0.98: 1: 0.987: 0.04 mixed, and adds the sucrose of end-product quality 10%, is medium with the absolute ethyl alcohol, with rotating speed 450r/min high speed ball milling 11h, makes mixture behind the dry 15h in ball mill.

Step 2: with the mixture that makes in the step 1 porcelain Noah's ark of packing into, in tube furnace, under argon gas atmosphere, be warming up to 350 ℃ with 15 ℃/min earlier, behind the insulation 5h, rise to 700 ℃ with 15 ℃/min again, sintering 10h treats to take out when product is cooled to room temperature, promptly gets end-product.

Claims (1)

1. a lithium ion battery is with mixing fluorine LiFePO ₄The preparation method of electrode material, the expression formula of this material is:

LiFe(PO ₄) _1-x/3F _x/C(x＝0～3)

It is characterized in that concrete steps are as follows:

Step 1: with analytical reagent LiOHH ₂O, FeC ₂O ₄2H ₂O, NH ₄H ₂PO ₄Mixing with fluoride, add carbon source, is medium with the absolute ethyl alcohol, and with rotating speed 300～450r/min high speed ball milling 10～15h, dry 10～20h makes mixture;

Step 2: with the mixture that makes in the step 1, under argon gas atmosphere, be warming up to 300～400 ℃ with 10～15 ℃/min earlier, behind insulation 5～10h, rise to 600～800 ℃ with 10～15 ℃/min again, calcining 10～20h, calcining is finished and is taken out after the afterreaction thing naturally cools to room temperature, obtains target product;

Wherein, LiOHH ₂O, FeC ₂O ₄2H ₂O, NH ₄H ₂PO ₄And the proportionate relationship between the fluoride is: (1.02-x): 1: (1-x/3): x, wherein x=0～3;

Described fluoride is LiF, NaF, KF, CaF ₂, MgF ₂Deng in one or more, it is in sucrose, glucose, the carbon black etc. one or more that carbon coats used carbon source, carbon coating ratio accounts for gross mass 2%～20%.

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